As it is not possible to provide a detailed scheme
of insulation for any specific case without inspecting the premises
and performing certain measurements, the observations given here
must necessarily be general and may not produce a significant
improvement in all instances.
Before embarking on a programme of supplementing
the inherent sound insulation of the separating wall, it is worth
inspecting the wall construction to determine whether there are
any specific weaknesses from a sound insulation viewpoint. Common
hidden leakage paths include spaces in the brickwork where joists
are supported, 'thin' areas of wall where recessed fittings are
located and noise transmission via the loft in some cases of very
lightweight ceilings. Such deficiencies should be rectified by
sealing and/or adding mass.
Improvements in separating wall insulation can
often be achieved by erecting a secondary leaf over the area of
the separating wall. Such a secondary construction might comprise
a minimum 32mm plasterboard skin, made up of 12.5mm and 19mm
plasterboard arranged to have staggered and sealed joints, on
a 75mm thick timber framework. The timber frame must not be fixed
directly to the separating wall but should be supported from the
floor, boundary walls and ceiling, the gap between the plasterboard
and the separating wall being at least 125mm. The cavity behind
the plasterboard should enclose a 50mm thick (or thicker) quilt
of mineral wool or glass fibre. Care must be taken to ensure that
a good seal is achieved between the plasterboard panels and with
the boundary walls, ceiling and floor. It will be appreciated that such
a treatment will result in the loss of floor area.
The improvement attainable in some cases by such
a method is of the order of 10 decibels, which would appear subjectively
as a halving of the loudness of the transmitted noise level. The
adequacy of such an improvement would depend on the particular
circumstances, eg individual sensitivity to noise and prevailing
background noise levels, and it is not certain that this level
of improvement would be obtained in all cases.
Other Sources of Information:
'The Building Regulations 2000 - Approved Document
E'.
BR 238 - CIRIA report 127 'Sound Control for Homes',
Section 4: Dwelling-houses and flats formed by material
change of use, pp 53-59.
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